% Yield of Sodium Carbonate
Introduction
Reaction stoichiometry is used to relate the amounts of reactants and products in a chemical
reaction. For example, consider the combustion of propane:
C3H8(g) + 5O2(g)  3CO2(g) + 4H2O(g)
This equation tells you that for every 1 mol C3H8 combusted, 5 mol O2 must react and 3 mol of
CO2 and 4 mol H2O must be produced. No matter how much propane is consumed, these ratios
must always be the same. Thus, it is possible to predict the number of moles of CO 2 that would
be produced if 40.0 mol O2 is reacted:
40.0 mol O2 *
3 mol CO2
5 mol O2
= 24.0 mol CO2
It is also possible to predict the mass of CO2 that would be produced from the combustion of
61.0 g of propane:
61.0 g C3H8*
1 mol C3H8
3 mol CO2
44.01 g CO2
44.11 g C3H8
1 mol C3H8
1 mol CO2
= 183 g CO2
183 g is the theoretical yield of CO2. The actual amount of CO2 collected will almost always be
less. There are a variety of reasons why the actual yield is less than the percent yield.
Sometimes the reaction is not allowed to finish. Sometimes a different reaction occurs, causing
byproducts. Sometimes you cannot collect all of the product generated. To account for these
difficulties, it is common to report the percent yield:
percent yield =
actual yield
theoretical yield
* 100%
If 125 g of CO2 were actually collected from the above reaction, the percent yield would be:
68.3% =
125 g CO2
183 g CO2
* 100%
Pre-Lab Exercise
Name: __________________________________________________________
Assume you perform the procedure outlined in the experiment “% Yield of Sodium Carbonate”.
The reaction is as follows:
NaHCO3(s)  Na2CO3(s) + CO2(g) + H2O(g).
You weigh out 1.4895 g baking soda (NaHCO3), heat it, and are left with 1.0026 g of solid
(Na2CO3)
1) Balance the reaction equation above.
2) Calculate the total theoretical mass of gases that should have been produced.
a)
How much CO2 gas should be produced from 1.4895 g NaHCO3?
b) How much H2O gas should be produced from 1.4895 g NaHCO 3?
c) How much gas altogether should be produced? (add them up)
2) Calculate the total mass of gases that was actually produced in the experiment. Remember you were
left with 1.0026 g Na2CO3 after the gases disappeared.
1) Calculate your percent yield of gases. The formula is:
percent yield =
actual yield
theoretical yield
* 100%
Procedure and Data Sheets
Name__________________________________________________________
In this experiment, you will study the stoichiometry of a reaction. You will determine the percent
yield of the decomposition of sodium bicarbonate. When you heat sodium bicarbonate, it
decomposes according to the following equation:
2NaHCO3(s)  Na2CO3(s) + CO2(g) + H2O(g)
Since two of the products are gases, the mass lost in the reaction is the mass of the gases. The
actual yield of gases will simply be the difference in the mass of the sample before and after the
reaction. The theoretical yield can be determined by stoichiometry.
1. Obtain a disposable aluminum tray and weigh to the nearest 0.01 g.
2. Add 1 to 2 g of NaHCO3 (sodium bicarbonate or baking soda) to the tray and weigh to the
nearest 0.01 g.
3. Gently tap the tray to spread out the NaHCO3 and place on a hot plate. Heat sample for
5 to 10 minutes on high, and then cool to room temperature.
4. Weigh the product of the reaction (Na2CO3) in the aluminum boat to the nearest 0.01 g.
Mass of
aluminum tray
Mass of
aluminum tray
and NaHCO3
Mass of
NaHCO3
Mass of
aluminum tray
and Na2CO3
Mass of
Na2CO3
(Actual yield)
Stoichiometry Calculation
2 NaHCO3(s)  Na2CO3(s) + CO2(g) + H2O(g)
With how much
NaHCO3 did
you start the
reaction in the
aluminum
boat?
*How much
Na2CO3 should
you have
produced?
How much
Na2CO3 did
you actually
produce?
**Determine
the % yield.
*Show your calculation here using conversion factors. Put a box around your final answer. Make
sure you include units.
**Use the formula in the introduction.
If you got what you should get, you would have a 100% yield. How did you do?
Post Lab Questions
1. Would insufficient heating cause the % yield to be lower or greater than 100%? Explain
2. As described in experiment, NaHCO3 decomposesat around 100oC to give Na2CO3, water and
carbon dioxide. At elevated temperature(around 850oC), Na2CO3 decomposes to give Na2O
and CO2. Sketch a graph of mass (y-axis) vs temperature (X-axis) for a NaHCO 3 sample that is
heated from room temperature to around 10000C.